An introduction to piezo MEMS oscillators

In addition to overcoming the higher native frequency challenge for quartz crystals and traditional MEMS, we also studied known quartz limitations such as activity dips, aging, vibration sensitivity, etc.

Activity dips

One of the known issues for crystal oscillators is activity dips that can cause intermittent failures. These failures affect both the frequency and the resistance (i.e., the Q) of crystal resonators. Activity dips are usually caused by interfering modes (e.g., by high overtone flexure modes) and are strongly influenced by the crystal’s drive level and load reactance. These activity dips are not present for MEMS oscillators since the MEMS resonators are designed to suppress undesired modes over temperature and process variations that can impair crystal-based oscillators.

Shock and vibration sensitivity

In addition, as part of the improved reliability, MEMS oscillators demonstrate enhanced semiconductor-grade shock and vibration resistance. Standard quartz devices are fragile since the crystal is housed within a metal or a ceramic package, allowing the crystal to be fractured by a shock of 50-100g. Manufacturers have to then implement specific storage, packing and shipping protocols for crystal devices to avoid careless handling.

pMEMS oscillator resistance to shock and vibrations were evaluated. The devices were easily able to survive more than 1500G of shock and 20G of vibration test as shown in figure 6.

In these tests, plastic packaged pMEMS resonators were placed together with quartz devices in temperature-controlled chambers. At 25°C, pMEMS devices have a frequency variation of less than ±2.5 ppm over a period of 21 months, which is better than the typical quartz performance of ±5 ppm – see figure 7.

Finally to demonstrate the performance of these high-performance sub-ps jitter (12kHz – 20 MHz) pMEMS oscillators in the real world, three applications were implemented for networking, FPGA and storage applications as shown below.

All of these pMEMS application demonstrations have been traveling at various shows around the world –see figure 9.

Figure 9: pMEMS oscillators demonstrated in three different applications

Click on image to enlarge

Other advantages of MEMS-based products include natural compatibility with surface-mount assembly processes and short lead times; this enables suppliers and users (electronic manufacturers) to hold smaller device inventory with reduced risk of supply shortages. IDT’s MEMS oscillators support low-voltage differential signaling (LVDS) and low-voltage positive emitter-coupled logic (LVPECL) outputs at frequencies of up to 625MHz, which is required in most communications, networking and high-performance computing applications.

Conclusions

A new class of pMEMS oscillators has been introduced for high-frequency, low phase noise (<1.0 ps) timing reference applications. The high performance, as well as compactness and stability of the pMEMS devices, has proven this technology to be a cost-effective and more reliable next-generation replacement for quartz crystal oscillators for the high-frequency frequency reference applications.

About the author

Harmeet Bhugra is a managing director at IDT and is responsible for the vision, growth and general management of the MEMS business - www.idt.com
Courtesy of EETimes Europe